The present invention relates to the filler gels used in cosmetic surgery for filling wrinkles.
Such gels are, for example, based on hyaluronic acid and are injected under the skin using a syringe.
It is important for the gel to be able to be injected easily using a syringe equipped with a fine needle, and for the implant thus injected to be able to be positioned in a suitable manner in the injection site according to the stresses applied by the practitioner, and then to adapt to the stresses and dynamics of the face.
The rheology of the gel is therefore an essential element that it is advisable to control if it is sought to obtain optimal results.
The rheological quantities of the gels that are customarily most used are the elastic modulus G′ and viscous modulus G″, the phase angle δ being connected to these quantities (tan δ=G″/G′). These data are obtained in oscillatory rheology and are normally measured for low oscillation stresses and amplitudes, i.e. in the linear viscoelasticity zone, where G′, G″ and δ are relatively constant; such a measurement does not reflect all of the mechanical stresses and deformations to which a filler gel is subjected depending on its function.
Attempts to use rheological measurements have to date not proved sufficiently predictive, and there is consequently a need to resolve this problem.
There is furthermore an advantage in having tools for characterizing and selecting gels in the laboratory, making it possible to avoid resorting to in vivo tests at the selection stage in the development of a product.
There is consequently a need to facilitate the development of a novel filler gel and in particular to be able to easily differentiate several gels in order to retain that or those having the most advantageous properties with respect to the desired result.